This application relates to the art of switches and, more particularly, to switches that automatically move from either a normally open or a normally closed position to the opposite position in response to a change in pressure or temperature. The invention is particularly applicable for use with rechargeable batteries and will be described with specific reference thereto. However, it will be appreciated that the invention has broader aspects and can be used with other devices where it is desired to open or close a circuit in response to an elevated pressure or temperature. The invention also will be described with reference to a switch assembly that responds to either pressure or temperature. However, it will be appreciated that the pressure and temperature responsive features do not necessarily have to be used together and that each feature is capable of independent use.
Circuit devices that respond to temperature and/or pressure are used with batteries to interrupt charging or discharging of the battery in the event of thermal runaway that may raise the battery internal pressure and/or temperature to undesirable levels. The circuit devices are intended to interrupt battery charging or discharging before undesirable temperature and/or pressure levels are reached. Arrangements also are used for venting the battery case responsive to an excessive internal pressure. Existing arrangements of this type are relatively complicated and/or have a relatively high resistance that reduces the efficiency of battery discharge and recharge.
A pressure and temperature responsive switch assembly includes a movable switch member that is in either a normally open or a normally closed position under normal temperature and/or pressure conditions. The switch member is of a bimetal material or of a shape memory alloy that responds to an elevated temperature by moving from the one normal position to the opposite position. A force transfer member such as a bumper is positioned between the switch member and a snap-acting foil diaphragm that responds to a predetermined pressure for moving the switch member from one position to the other in response to an elevated pressure acting on the opposite side of the diaphragm from the bumper. The foil diaphragm itself may rupture in response to excessive pressure for relieving same in the event increasing pressure is not interrupted by operation of the switch.
In a preferred arrangement, the temperature responsive switch member is of shape memory alloy that has a deformed shape at normal temperatures and a recovered shape at an elevated temperature. The switch member of shape memory alloy may have either a normally open or a normally closed position when it is in its deformed shape at normal temperatures, and automatically moves to the opposite position at an elevated temperature by changing to its recovered shape.
In other arrangements, the temperature responsive switch member is a bimetal that may have either a normally open or a normally closed position at normal temperatures, and automatically moves to the opposite position at an elevated temperature.
In one arrangement, a movable bumper integral with an insulator that supports a base portion of the switch member cooperates with a pressure responsive snap-acting foil diaphragm to impart movement to the movable switch member. An attachment ring secured to a housing member holds the support insulator in position.
A switch assembly that uses the bimetal or shape memory switch member may be attached to a housing member such as the lid of a battery case or a battery case itself, or to a housing for another device that may produce an excessive temperature and/or internal pressure. A switch assembly in accordance with the present application responds to an elevated pressure or temperature by interrupting the charging or discharging state of the battery before the pressure or temperature become excessive.
In one arrangement, a housing member has a fixed contact attached thereto and a snap-acting foil diaphragm normally closes a pressure port in the housing member adjacent the fixed contact. In its deformed shape at normal temperatures, a switch blade of shape memory metal has an end portion engaging the fixed contact and moves to an open position out of engagement with the fixed contact in response to an elevated temperature by assuming its recovered shape.
A movable dielectric force transfer member such as a bumper is located between the pressure responsive snap-acting foil diaphragm and the switch blade, and the blade is movable with the diaphragm and bumper in response to an elevated pressure for placing the switch blade in an open position. In one arrangement, the switch blade is on a switch blade member that has a base portion supported by an annular support insulator attached to the housing member by an attachment ring. A metal terminal plate is held to the support insulator against the base portion of the switch blade member, and an electrical lead is attachable to the terminal plate.
In one arrangement, the fixed contact may be a conductive foil located on the housing member outwardly of the pressure port that normally is closed by the snap-acting foil diaphragm.
In another arrangement for a normally closed switch, the switch member may be a bimetal that is a bowed strip or a disc having a central portion cooperable with a movable force transfer member such as a bumper. The peripheral edge of the disc or the end edges of the strip switch member engage a metal terminal plate, and a conductive foil attached to the housing member provides a fixed contact that is positioned in engagement with the central portion of the switch member between the switch member and the bumper. The switch member may be a curved bimetal strip or a dished disc that opens a circuit by snapping to a reversed curvature in response to an elevated temperature so that the central portion of the bimetal engages the metal plate and its peripheral edge or end edges engage an electrical insulator positioned on the conductive foil fixed contact and the housing member. Movement of the snap-acting foil diaphragm and bumper responsive to an elevated pressure also causes the normally closed switch member to move to a reversed position for opening a circuit.
In a modified arrangement for a normally open switch, an insulator may be positioned between the disc or bowed strip bimetal switch member and the bumper to provide a normally open circuit. Upon reverse bowing of the switch member, its central portion opposite from the bumper engages a metal terminal plate and its peripheral edge or end edges engage a conductive foil fixed contact located outwardly from the insulator and the bumper to provide a closed circuit position at an elevated temperature or pressure.
In still another arrangement, a disc or bowed strip temperature responsive switch member that may be of shape memory metal or a bimetal has its peripheral edge or end edges engaging a metal plate and a central portion engaging a fixed contact to complete a circuit. The switch member automatically changes shape to move out of engagement with the fixed contact in response to an elevated temperature. Pressure responsive snap-acting foil diaphragms cooperate with a movable force transfer member surrounding the fixed contact to separate the switch member from the fixed contact in response to an elevated pressure.
The improved sensing switch of the present application for sensing elevated temperature and/or temperature conditions may be used in a multi-cell package for such applications as electric vehicles. A sensing switch is associated with each individual cell and disables an individual cell that may experience an elevated pressure or temperature while leaving the remaining cells in operation.
In all of the arrangements, the snap-acting foil diaphragm may be rupturable in response to excessive pressure for relieving same. Thus, even if the switch does not operate responsive to an elevated pressure or temperature, or if the pressure continues to build despite operation of the switch, rupturing of the diaphragm would vent the excessive pressure.
Although the switch may be designed to revert to its original position upon dissipation of an elevated temperature or pressure, it preferably is designed as a one-shot fuse and remains in the position to which it is moved by an elevated temperature or pressure following dissipation of the elevated temperature or pressure.